Like water, electricity, and natural gas, compressed air—the so-called “fourth utility”—is vital to the operation of many facilities. And like the other utilities, compressed air can also be one of a plant’s biggest operating expenses.

Energy tops the list of items that account for the total cost of compressed air use, says Richard Stasyshan, technical director of the Compressed Air & Gas Institute, a source of technical and educational information for industry. In fact, the energy used by a typical compressor over its lifespan usually costs several times more than the purchase price of the compressor. “So it’s essential that people focus on operating their compressed air systems more efficiently,” he says.

In addition to being smarter about how they use compressed air, plant personnel can take advantage of a number of technologies aimed at boosting compressed air system efficiency. Call it an effective one-two punch for knocking down the cost of compressed air use. Stasyshan says the savings can range from thousands of dollars to in excess of $100,000 a year.

Commonsense Steps

Some simple and commonsense steps can yield significant savings. For example, turning off compressors so they are not running at times when they are not needed—possibly at night or on weekends, depending on a facility’s shift patterns—can reduce energy bills by 20%, Stasyshan says.

In addition, he says, plants should eliminate what he calls “inappropriate” uses of compressed air. These include using high-pressure air for cooling and other tasks that can be accomplished with much lower air pressure.

Stasyshan also recommends a major effort to find, fix and prevent air leaks. “Since energy is needed to produce compressed air, any air leak is money wasted,” he says. For example, a quarter-inch air leak at 100 psi could cost a plant more than $2,500 a year.

A master system controller can boost the efficiency and reduce the operating cost of a system with two or more compressors. Image credit: Ingersoll RandTo prevent leaks, Stasyshan encourages plant personnel to look inside their piping system. A clean, dry pipe is a sign of good-quality air and no corrosion issues. On the other hand, the presence of dust and sludge in a compressed air piping system will cause corrosion, which in turn will increase the number of leaks. To prevent this kind of trouble, he recommends using dried and filtered compressed air to keep piping clean.

As for finding leaks, this can be done during walkthrough inspections that target easy-to-spot problems. For example, plant personnel may hear hissing air leaks during a walkthrough held on a weekend or holiday when the plant isn’t running.

But finding leaks won’t always be easy. In fact, Stasyshan says that roughly 80% of leaks are not audible, meaning that third-party leak-detection help may be necessary.

Such help is offered by Ingersoll Rand, among others, which checks facilities using an ultrasonic device that can detect air leaks the human ear can’t hear. The ultrasonic detector also finds leaks that are too far away to be heard (in pipes high overhead, for example) and those unheard because of background machinery noise, says Chad Larrabee, North American director of services marketing for Ingersoll Rand Compressed Air Systems and Services.

More Storage

Another tool that Larrabee favors is compressed air storage. “Storage is a wonderful thing,” he says. “It’s just a tank, so you don’t have to repair it or maintain it. But it solves many problems.”

When system pressure drops, for example, plant personnel often respond by turning on more energy-consuming compressors. “But we say more is better in a compressed air system only when it comes to storage,” says Larrabee, who recommends 5-10 gallons of storage per cfm rating of a compressor. “Don’t try to solve your problem with more power, solve it with more storage.”

Think of a compressed air tank as a battery-like source of stored energy. “If a big air user takes down the pressure of the whole plant for a few seconds, the battery in the system—the storage—can take care of the problem instead of the compressor trying to do it.”

Both Larrabee and Stasyshan suggest that plant personnel resist the urge to turn up the pressure to deal with problems in a compressed air system. Instead, Stasyshan says they should look for ways to reduce pressure, because every 2 psig pressure reduction cuts energy consumption by 1%.

Expert Assessments

Larrabee claims that he and his colleagues can reduce the pressure in most plants when they do a system assessment. “Many times we find that people keep jacking up the pressure to overcome a systemic problem in their control scheme,” he says. “Or we’ll find a piece of equipment that [supposedly] needs 90 psi at the intake, but the component doing the work is being actuated at something as low as 40 psi.”

Expert assessments of compressed air systems are often referred to as “compressed air audits.” Audits can be done by the manufacturer of a facility’s compressed air equipment or by an independent auditor.

Among the things an auditor looks for air leaks, compressors that can be turned off and ways to reduce system pressure such as adding storage or flow controllers. Auditors also hunt for unregulated air lines used for purposes that don’t require high-pressure air. “If you’re using an air line for a cleaning task like blowing off cuttings, you don’t need air coming out at the system pressure of 95 psi,” Stasyshan says. “You can do that at 15 psi. So you can save some money by putting a 15 psi regulator on that line.”

Better Technology

Plant managers looking for savings should also consider upgrading their compressed air technology. Stasyshan says that new piping systems allow leak-free connections, while the latest screw compressors feature rotors cut to the tightest of tolerances, making the air ends produced today the most efficient ever.

Another upgrade option for plants running multiple compressors is a master system controller, which Larrabee likens to an orchestra conductor. This controller “tells each of the compressors when it’s needed and then controls each one based on the compressed air demand,” he says. “We always say that if you have two or more compressors in a system and you don’t have a master system controller, you’re running at an elevated pressure or you’re running too many compressors or you’re running the wrong combination of compressors.”

For those interested in cutting compressed air use, there may be no bigger target than air-blowing applications. According to Parker Hannifin Corp., these applications—which include cooling, drying and swarf removal—consume almost half of all compressed air used in plants.

Aimed at these activities, the company’s Air Saver product is a switching valve intended to replace existing valves that control air blowing. The Air Saver converts continuous airflow into a series of “on” and “off” pulses that last a fraction of a second. When the airflow is off, no air is consumed. The cumulative amount of time airflow is off can cut air consumption in half in air-blowing applications, Parker Hannifin claims.

For a plant, the result can be a halving of monthly air-blowing power costs and carbon dioxide discharge, says Richard McDonnell, market development manager for Parker Hannifin’s North American pneumatic division.

More options exist for reining in compressed air use and costs. But considering those mentioned above could be a good first step toward the creation of a more efficient, sustainable and profitable plant.